1. Field of the Invention
This invention relates to a stable, one component, curable, amino resin binder system useful in the production of fiberboard and other wood and paper products and to its method of manufacture.
2. Discussion of the Prior Art
Curable amino resin binder systems comprised of an aqueous solution of urea, formaldehyde and melamine are known in the art and have met with substantial commercial success in the production of fiberboard.
U.S. Pat. No. 3,629,176 to Shriver, teaches an amino resin binder system useful for the production of fiberboard and plywood. Melamine, and optionally urea and water, are added at a temperature less than about 5.degree. C. to a urea-formaldehyde reaction product to obtain a slurry which can be employed to bond fiberboard and the like. This system is relatively unstable and therefore must be formulated in the fiberboard plant since the solids of the slurry will separate out after a relatively short period of time thereby precluding shipment of such a product as a one-component, ready-to-use system.
U.S. Pat. No. 3,458,464 to Shriver et al. discloses aqueous urea-formaldehyde-melamine concentrates in which melamine and urea are added to an aqueous formaldehyde solution which is heated and then concentrated after cooling. Athough it is suggested in this patent that urea and melamine may be dissolved in the solution to obtain a reaction mixture useful in producing adhesives, molding powders and fabric-treating resins, the concentrate itself contains a very large amount of formaldehyde in order to increase its stability while containing a very small amount of melamine. Consequently, there is an odor problem associated with the large amount of formaldehyde. The system as envisioned in the Shriver et al. patent is at least a three-component system wherein urea and melamine plus the urea-formaldehyde-melamine concentrate are employed. Moreover, it has been found that the product of Shriver et al. becomes unstable (i.e., becomes solid) after about three days storage.
U.S. Pat. No. 2,085,492 to Ellis discloses carrying out the reaction of urea and acid-containing methanolic formaldehyde in the presence of additional methanol solvent or other volatile diluents which are miscible with water in order to lessen the thermal effect of the reaction and to obtain a soluble product. The solvent is recovered after the reaction is completed.
Attempts have also been made to stabilize the amino resin slurry. For example, U.S. Pat. No. 3,826,770 to Christensen et al. discloses urea-formaldehyde aqueous concentrates useful in the manufacture of particle board and the like, which contain an ionized inorganic salt and optionally an alcohol as a stabilizer. This system is not a solution, does not contain melamine, and is not as stable as the binder systems of the present invention.
Australian patent application No. 60,444 to Montecatini discloses a melamine-formaldehyde solution in a hydroalcoholic medium, such as methanol, which contains an aromatic sulfamide as the stabilizing agent and British Plastics, August 1953 (pages 306-308) discloses aqueous melamine-formaldehyde syrups which are stabilized against gellation and precipitation by the incorporation of an alcohol and borax. These solutions or syrups do not contain urea and therefore are significantly easier to stabilize than a binder system containing urea.
Most of the above-identified prior art references have contributed to the art by teaching the production of slurries or solutions having various degrees of stability. But, none of these references teach the preparation of a binder solution that would be stable for a long enough period of time so that it could be shipped, as one component, to fiberboard manufacturing facilities and stored for commercially practical times.
U.S. Pat. No. 3,891,590 to Sundie et al. advanced the art by teaching the preparation of a two-component system which could be stored and shipped separately, from which curable amino resins could be easily prepared without serious mixing problems and duplication of mixing machinery. The amino resin system taught in U.S. Pat. No. 3,891,590 is not necessarily suitable for an exterior grade fiberboard whereas U.S. application No. 696,159, filed June 14, 1976 discloses an amino resin which is suitable for exterior grade fiberboard.
The present invention solves the prior art problem of stability of the amino resin binder system as well as the problem of requiring the shipment of at least two separate components for preparing a stable binder suitable for commercial use.